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UL
GROUND RESISTANCE TESTER
UL requires that an electrical system using a metal chassis earth ground connection
have a resistance of less than 0.1 ohms. This resistance must be tested with
actual line current in excess or 10 amps. The circuit shown uses a couple of
LEDs to indicate if in fact the resistance is less than 0.1 ohms. It uses a
modified transformer to produce a 2.5vac output with at least 10 amps of supply
current.
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Accurately measure resistance with less than perfect components -
11-Nov-04 Issue of EDN For transducers, such as strain gauges or
thermistors, you must accurately and inexpensively measure resistance
using circuitry built with imperfect components and in which gain and
offset errors can significantly limit the accuracy of ohmic
measurements. The right circuit topology makes it possible to eliminate
most error terms while measuring ohms, leaving the accuracy to be
determined by jus.... [Design Idea by Dave Van Ess, Cypress
Semiconductor]
Better Approach to Designing an RTD Interface with a SpreadSheet -
02/07/08 Issue of EDN RTDs (resistance-temperature detectors] are
the preferred sensor choices for designs requiring precision.....
[Design Idea by Robert S Villanucci, Wentworth Institute of Technology,
Boston]Voted best of Issue!
Grounded resistor tunes oscillator - 29-May-03 Issue of EDN To
vary the frequency of any sine-wave oscillator, you should use a pair of ganged
variable resistors, and you should thoroughly match their characteristics over the
entire variation range to satisfy the oscillator's balancing conditions.
This restriction leads to problems in the tuning range and high cost, thereby
limiting the range of applications.... [Design Idea by Vladimir Tepin, Taganrog,
Russia]
Optimize linear-sensor resolution - 7-Mar-02 Issue of EDN A wide
variety of sensors and transducers of physical phenomena work via the mechanism of
variable resistance. These devices sense temperature, light, pressure, humidity,
conductivity, and force, for example. Such sensors measure the physical parameter
of interest by reading out the inherent parameter-sensitive resistance or
conductance.... [Design Idea by Steve Woodward, University of North Carolina,
Chapel Hill, NC]
UL Ground Resistance Tester - UL requires that an electrical system
using a metal chassis earth ground connection have a resistance of less than 0.1
ohms. This resistance must be tested with actual line current in excess or 10
amps. The circuit shown uses a couple of LEDs to indicate if in fact the
resistance is less than 0.1 ohms. It uses a modified transformer to produce
a 2.5vac output with at least 10 amps of supply current.... [Designed by David A.
Johnson]
